Residual-Year Corn Response to Liquid Swine Manure Nitrogen Applied to Soybean.

Liquid swine (Sus scrofa domesticus) manure (LSM) is a valuable source of plant nutrients to be utilized for crop production.  However, there has been no study investigating the N response of corn (Zea mays L.) to potential residual N effects of LSM applied to a preceding soybean [Glycine max (L.) Merr.] crop.  Objectives of this study were to evaluate response of soybean to LSM application, potential for post-harvest soil profile NO₃-N accumulation, and residual-year LSM N response in corn.  On-farm trials were conducted at eight different sites across Iowa from 2000 to 2003.  Three application rates of control, low, and high LSM were applied to soybean. In the following year corn, four fertilizer N (FN) rates were applied within each prior-year LSM rate.  The LSM significantly increased soybean grain yield (GY) at 63% of sites, with no GY reduction at any site.  Post-soybean harvest soil profile NO₃–N increased at four sites with LSM application, with a mean across site 12 and 24 kg NO₃–N ha^-1 increase for the low and high LSM rates, respectively.  Residual-year corn GY was increased at 71% of sites from the prior-year LSM N application. Corn leaf relative chlorophyll meter (RCM) values were also increased with the prior-year LSM N, and end of season lower corn stalk NO₃–N (CSNT) increased with the prior-year LSM, but only when FN was also applied. The residual-year N supply to corn was estimated at 11% of the total LSM-N applied to soybean using the GY and RCM responses to FN rate, approximately the mean post-soybean harvest profile NO₃–N ha^-1 increase with each LSM rate.  Liquid swine manure application to soybean can be a viable nutrient management practice; however, total-N application should be at a rate to minimize residual NO₃–N buildup and carryover to future crops.